The present invention relates generally to a variable intake control system for an internal combustion (IC) engine. More particularly, it pertains to an intake system that employs cycle-by-cycle control of airflow and compressible fluid resonance techniques to efficiently use or enhance intake gas pressure pulses when charging the cylinders.
Camless variable valve actuation systems have been developed to control engine intake valves and exhaust valves using electrohydraulic and electromagnetic technology rather than conventional mechanical camshafts to provide variability in the charging process that cannot be obtained with fixed camshaft actuation of the engine valves. But these camless valve actuation systems are costly and complicated.
Various techniques are used to improve the intake gas supply of reciprocating piston-type internal combustion engines. For example, U.S. Pat. No. 4,513,699 describes an intake gas resonance system associated with a group of engine cylinders whose suction strokes do not significantly overlap. The system includes a resonator communicating with intake openings of the cylinders. The system further has a resonance tube communicating with the resonator. The resonance tube has a length portion terminating at the resonator vessel and having cross-sectional areas increasing towards the resonator vessel. The cross-sectional area taken at the end of the resonance tube where it joins the resonator vessel is at least 1.2 times greater than the minimum cross section of the resonance tube. The distance between the end of the resonance tube joining the resonator vessel and an oppositely located inner wall face of the resonator vessel is greater than the diameter of a circle whose area equals the cross-sectional area taken at that end of the resonance tube.
There is need for a simple, low cost technique to improve engine intake gas charging control, in which intake and exhaust valves are controlled by single or double lobed camshafts, preferably camshafts designed to produce the longest valve open periods that are required anywhere in the engine operating map. Such cam timing features are best suited for optimal high speed, high power engine operation, and are accomplished with fixed cam timing. However, these long opening periods will be detrimental during other modes of engine operation, at lower speeds and loads, and thus require additional controls to provide variability which produces optimal performance at all points in the operating map.
There is a further need also to enhance exhaust gas recirculation (EGR) into an IC engine using conventional structural components and simple electronic control strategies. Additionally, a two stroke IC engine having no engine intake or exhaust valves would be controlled during each engine cycle to prevent back flow of engine exhaust gas from the exhaust runner into the combustion cylinder.
It is desirable, therefore, to provide means for improving the air handling capabilities of a naturally aspirated engine using inexpensive components that do not require extensive modification to the valve train system of the engine.